1. Field of the Invention
Priority is claimed from Japanese Patent Application No. 2003-408906, filed Dec. 8, 2004, the contents of which are incorporated herein by reference.
The present invention relates to a squib (ignition apparatus) of an occupant protection apparatus that is mounted in a vehicle or the like.
2. Description of Related Art
In recent years, occupant protection apparatuses that use supplemental restraint systems such as airbags and pretensioners in order to protect an occupant of a vehicle or the like have become widespread. In these occupant protection apparatuses, a supplemental restraint system is placed in a required location, and when an impact acts on a vehicle, this impact is detected by a sensor and the supplemental restraint system protects the occupant by temporarily restraining the occupant such that the occupant does not collide with an object in the vehicle interior.
Conventionally, in order to reduce the number of supplemental restraint systems placed in a vehicle, a connection between a control unit that controls the supplemental restraint systems and a squib that operates the supplemental restraint systems has been, for example, a simple 1 to 1 connection (i.e., a peer to peer connection). However, recently, due to the placement of supplemental restraint systems in various locations of a vehicle there has been a trend towards the number of supplemental restraint systems increasing. As a result, there have been demands for the connecting wires (i.e., harnesses) that connect control units and control units with squibs of supplemental restraint systems to be reduced as much as possible. Therefore, a method has been proposed (for example, in Japanese Patent Application Laid-Open (JP-A) Nos. 10-154992 and 2000-1249321) in which a connection between a control unit and a squib of a supplemental restraint system is made using a bus wire that is capable of transmitting power and control signals, and a plurality of supplemental restraint systems that are connected to the bus wire are controlled by a single control unit using ignition control based on communication that specifies the relevant squib.
On the other hand, in order for a squib to be connected to a bus wire and receive ignition control based on communication from a control unit, it is necessary for the squib side to be provided with a communication circuit that is used to communicate with the control unit, and an ignition circuit that supplies power to an ignition element in order to ignite an explosive that causes the supplemental restraint system to operate. In this squib, a control IC that controls communication and ignition is placed between the ignition element and an external connection terminal that is used to connect the squib to the bus wire (see, for example, Japanese Patent No. 3294582).
However, in a conventional method of connecting a control unit to a squib for a supplemental restraint system using a bus wire, although it is possible to control a plurality of supplemental restraint systems efficiently using a single control unit, the only connecting wire that transmits power or control signals to the plurality of supplemental restraint systems is the bus wire. Therefore, the problem arises that the transmission of power or control signals via the bus wire needs to be extremely reliable. In particular, when the squib is provided with a communication circuit and an ignition circuit, as is the case with a conventional squib, sufficient consideration needs to be given to ensuring that the bus wire is not electrically affected by the squib that is provided in the supplemental restraint system being operated, and the problem arises that the reliability of the bus wire needs to be increased still further.
The present invention was conceived in view of the above described circumstances and it is an object thereof to provide a squib that, when causing a supplemental restraint system to operate, does not electrically affect an external signal wire that supplies power and control signals.